#' Calculate the atmospheric emissivity.
#' 
#' Calculate the atmospheric emissivity.
#' 
#' @param Tk value of air temperature in Kelvin.
#' @param RH value of relative humidity in fraction.
#' 
#' @return atmospheric emissivity.
#' 
#' @author Ana Casanueva (05.01.2017).
#' @details Reference: Oke (2nd edition), page 373.


emis_atm <- function(Tk, RH){
  
  e <- RH * esat(Tk)
  emis_atm <- 0.575 * e ^ 0.143
  return(emis_atm)
}